The present invention generally relates to medical devices and methods for ablating living tissue. More particularly, the present invention relates to radio frequency ("RF") ablation catheters and methods for using the same to create lesions within the heart.
Atrial fibrillation is a condition in the heart in which abnormal electrical signals are generated in the endocardial tissue to cause irregular beatings of the heart. A proven protocol for successfully treating this condition is open heart surgery (sometimes referred to as the "maze" procedure) where several long (i.e. approximately 2-10 cm) lesions are created in the endocardium within the upper chambers of the heart ("atria"). These lesions block the flow of excess electrical impulses within the atria and allow the impulse from the sinus node to properly regulate heart contraction.
However, because open heart surgery is highly invasive and requires a lengthy patient recovery period, alternative methods for making lesions have been recently explored. One such alternative is the use of ablation catheters that includes one or more electrodes.
Typically, an ablation catheter is advanced into the heart via the patient's vessels. When the electrodes are placed in the desired position within the heart chamber, radio frequency ("RF") energy is supplied to the catheter thereby burning lesions into the endocardium.
Initial designs for ablation catheters generally comprised of an elongated shaft in which an electrode is mounted onto its distal end. Either point and linear lesions could be formed with these catheters by manipulating the placement of the tip. However, because of the tendency for the tip electrode to overheat and to lift off the tissue surface during ablation, creating suitable lesions using these catheters have been difficult.
New catheter designs attempted to mitigate these disadvantages. One improvement is the addition of a mechanism to cool the tip electrode during use to minimize the risk of embolism from overheated blood. Such cooled tip ablation catheters are described in U.S. Pat. Nos. 5,423,811 and 5,545,161 both of which are incorporated in their entireties herein by reference. Although these catheters mitigate the overheating problem, the tendency for the tip electrode to form uneven linear lesions still remains.
Another improvement is the substitution of the tip electrode for a series of electrodes to form a linear ablation section on the catheter. Illustrative examples of such ablation catheters are described in pending U.S. application Ser. No. 08/965,353 filed Nov. 6, 1997, now U.S. Pat. No. 5,895,417 entitled "DEFLECTABLE LOOP DESIGN FOR A LINEAR LESION ABLATION APPARATUS" by inventors Mark L. Pomeranz, Troy J. Chapman, Scott Tedder, Darren R. Sherman, and Steven C. Anderson, pending U.S. application Ser. No. 08/680,426 filed on Jul. 15, 1996, now U.S. Pat. No. 5,882,346, entitled "SHAPABLE CATHETER USING EXCHANGEABLE CORE AND METHOD OF USE" by inventors Mark L. Pomeranz and Peter Park, and allowed U.S. application Ser. No. 08/611,656 filed on Mar. 6, 1996, now U.S. Pat. No. 5,800,482, entitled "APPARATUS AND METHOD FOR LINEAR LESION ABLATION" by inventors Mark L. Pomeranz, Troy J. Chapman, Darren R. Sherman, and Mir Imran all of which are also incorporated in their entireties herein by reference.
These catheters facilitate the formation of suitable linear lesions by providing additional surface area for distributing RF energy. Although linear lesion catheters are a significant improvement over tip electrode catheters, breaks still occasionally occur due to the difficulty in maintaining sufficient contact between the ablation section and the tissue surface.
The impact of these breaks may be generally mitigated by forming point lesions at these sites in a follow up procedure. However, since linear ablation catheters are not generally suited to form point lesions, the follow up procedure typically requires removing the existing linear ablation catheter from the patient and substituting it for a tip electrode catheter. Because this catheter exchange may cause additional trauma to the patient as well as increase the overall length of the procedure, a need exists for an ablation catheter that combines the functionalities of both the tip electrode and the linear ablation section.